SiC has a wide band gap and a maximum insulation electric field one order of magnitude higher than that of silicon (hereinafter abbreviated as Si), and hence is expected to be applied to a next generation power semiconductor element. SiC is used for various electronic devices by using single crystal wafers referred to as 4H-SiC or 6H-SiC, and is considered to be particularly suitable for a high temperature and high power semiconductor element. Each of the above described crystals is an alpha phase SiC formed by laminating a sphalerite type crystal and a wurtzite type crystal. In addition, a prototypic semiconductor is also manufactured by using a beta phase SiC referred to as 3C-SiC. Recently, a Schottky diode, a MOSFET (metal oxide semiconductor field-effect transistor), a thyristor and the like are trially manufactured as the power semiconductor element. It is confirmed that such prototype elements exhibit extremely excellent characteristics as compared with conventional Si semiconductor devices.
In the semiconductor device using SiC, especially in a MOSFET having a channel formed on a surface of a SiC substrate, the surface formed by high temperature annealing is conventionally used as the channel. However, irregular recessions and projections exist on the surface of the SIC substrate obtained by the high temperature annealing. For this reason, the interface state density is increased, to thereby cause carrier mobility to be reduced, which results in a problem that the characteristics of the semiconductor device is deteriorated.
A technique for making it possible to solve this problem to a certain degree is disclosed in, for example, Japanese Patent Laying-Open No. 2000-294777 (Patent Document 1). In the above described Patent Document 1, a flat part (terrace surface) between bunching steps produced at the time of annealing after ion implantation is used for the channel part of a field-effect transistor, such as a MOSFET. Specifically, a SiC substrate is annealed at a temperature of 1600° C. in an atmosphere of Ar (argon) for one hour. As a result, steps are formed to gather each other on the surface of the SiC substrate, so that bunching steps are formed to make a flat part formed between the bunching steps. This flat part is used as the channel part of the MOSFET.
Patent Document 1: Japanese Patent Laying-Open No. 2000-294777